1. Field of the Invention
The present invention relates to a backlight used for a liquid crystal display.
2. Description of the Related Art
As is known, liquid crystal displays (LCDs) may be provided with a backlight for making the displayed information discernible. A backlight may include two fluorescent lamps, inverters, etc. One of the lamps may be arranged along the upper edge of the LCD panel, while the other lamp along the lower edge of the panel. Based on predetermined pulse signals, the inverters supply driving voltage to the lamps. To be precise, this voltage supply is performed only in response to the on-periods of the pulse signals. As a result, the two lamps are simultaneously turned on and off (the so-called xe2x80x9cchopping controlxe2x80x9d). The adjustment of brightness of the LCD panel is performed by changing the ratio of the length of the on-period to the length of one cycle of the pulse signal (one cycle consists of one on-period and one off-period). When the ratio is 90% for example, the brightness of the monitor may be the maximum. As the ratio decreases, the monitor brightness also decreases accordingly. Then, when the ratio is 50% for example, the monitor brightness may be the minimum.
The conventional LCD has been found disadvantageous in the following respect.
In the chopping control, as stated above, the two lamps are turned on and off simultaneously (i.e. in the same phase). In this manner, unfavorably, the monitor of LCD may start flickering when the above-mentioned ratio becomes smaller than 50%. This means that the dynamic range of the monitor brightness cannot be sufficiently wide.
The present invention has been proposed under the circumstances described above, and its main object is to provide an LCD backlight capable of providing an LCD with a wider dynamic range of the monitor brightness without compromising the information-presenting quality.
According to the present invention, there is provided a backlight for a liquid crystal display, which includes: N light emitting units to be turned on and off based on pulse signals of a predetermined cycle including an on-period and an off-period, where N is an integer equal to or greater than 2; and a phase controller for controlling a phase of each of the pulse signals. The on-periods of the respective pulse signals are phase shifted to each other.
Preferably, the on-periods of the respective pulse signals may be phase shifted by 360xc2x0/N.
The backlight of the present invention may further include a rectangular light guide provided with a pair of parallel edges along which the light emitting units are arranged.
Preferably, each of the light emitting units may be provided with a cold cathode tube.
Preferably, the light emitting units may be operated in at least three modes including a high brightness mode, a standard brightness mode and a low brightness mode. In the lower brightness mode, the on-periods of the respective pulse signals do not overlap each other.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.